1. Field of the Invention
This invention relates to a mixing box for an air condition system such as that shown in FIG. 1. The purpose of the system is to maintain a comfort condition, for example, a dry bulb temperature of about 75 degrees F., a suitable relative humidity and an air circulation rate not less than 0.4 cubic foot per minute per square foot of floor space (CFM/SF), for occupants of a room 10. The system includes a duct 11 and a flexible line 12 through which primary, conditioned air from a riser 13, is circulated through a mixing box 14*, and downwardly through a grill 15 into the room 10. The conditioned air flowing through the duct 11 into the mixing box 13 is typically at a temperature of about 50 degrees F., and bust be delivered to the room 10 at a rate adequate to provide ventillation or fresh air. The minimum ventilation requirement varies, according to code, and might be, for example, 0.05 CFM/SF. Hence, air must be supplied to the room 10 at the minimum circulation rate of 0.4 CFM/SF, and must contain the minimum ventilation, e.g., of 0.05 CFM/SF of primary air. Where a single mixing box 14 serves a room 10, all of the required ventilation air must be supplied therethrough. However, when several mixing boxes serve a single room or zone, some of the boxes can furnish all of the required ventilation air, at least under some conditions of operation, while the others merely recirculate air. FNT *The instant invention involves details of construction, operation or both of the mixing box 14; these details are not shown in FIG. 1.
The mixing box 14 is positioned within a plenum 16 between a false ceiling 17 for the room 10 and a floor 18 of a room (not illustrated) thereabove. Air within the plenum 16 is heated, for example, to approximately 85 degrees F. by air rising from the room 10 through openings 19 in diffuser panels 20 of the lighting fixtures 21, and then through openings 22 in reflectors 23 of the lighting fixtures 12 and into the plenum 16. Air so circulated from the room 10 through the lighting fixtures 21 and into the plenum 16 is heated by the lights in the fixtures 21, which are shown as fluorescent tubes 24, so that the plenum 16 is a source for heated air. Additional, or alternate, heat sources, such as ducted hot air which might be at a temperature of 110 degrees F., can be positioned within the plenum 16 to augment the heat provided by the lights 24 in the fixtures 21.
The load in the room 10 can very substantially from time to time depending on such factors as the occupancy of that room at a given time, the load imposed by the lights 24, computers, copiers, and other equipment that may be used within the room 10, and the load that may be imposed thereon by solar energy. Accordingly, the mixing box 14 is required to maintain the desired comfort temperature of 75 degrees F. notwithstanding variations in the air conditioning load which occur from time to time for the indicated and other reasons.
2. Description of the Prior Art
Numerous mixing boxes* of the induction type have been suggested. In some such boxes, for example, the rate at which primary conditioned air is delivered to the mixing box 14 can be varied, with a compensating variation in the rate at which a flow of air, for example from the plenum 16 and/or from the room 10, is induced into the mixing box for mixture with the primary air, so that a mixture of supply air flows from the box at a substantially constant rate not less than the minimum circulation rate, but at a temperature which varies depending upon the proportions of primary conditioned air and induced air in the mixture. It has further been suggested that primary conditioned air can be by-passed around the induction portion of a mixing box to provide a maximum flow of primary conditioned air, with no induction for times of peak load on an air conditioning system. FNT *See, for example, U.S. Pat. Nos. 3,114,505; 3,390,720; 3,516,606; 3,583,477; 3,604,625; 3,610,522; 3,611,908; 3,823,870; 3,883,071; 3,929,285; and 4,084,389.
U.S. Pat. No. 3,883,071 discloses a mixing box which receives and delivers to the room 10 primary conditioned air at a rate which is varied between a maximum, not less than the minimum circulation rate, and a predetermined lesser rate, the minimum ventilation requirement, as the air conditioning load on the room 10 varies between a maximum and an intermediate load. The apparatus includes an induction nozzle for inducing a flow of air from the plenum 16 and/or from the room 10, for mixture with primary conditioned air; the resulting mixture is delivered as supply air.
U.S. Pat. Nos. 3,929,285 and 4,084,389 both disclose mixing boxes which use a continuously operating fan, positioned downstream from the mixing region, rather than an induction nozzle, to induce air flow by drawing supply air from the mixing region for delivery to the room 10 at a constant rate not less than the minimum circulation rate. U.S. Pat. No. 3,929,285 also disclose apparatus wherein the rate at which primary conditioned air is delivered to the room 10 is varied between a maximum, not less than the minimum circulation rate, and a predetermined lesser rate, the minimum ventilation requirement, as the air conditioning load on the room 10 varies between a maximum and an intermediate load. When the air conditioning load on the room 10 is below the intermediate load, primary conditioned air continues to be delivered at the predetermined lesser rate while an induced flow from the plenum 16 and/or room 10 includes heated air, as required, for temperature control.